1. Related Applications
This application is related to copending U.S. patent application Ser. Nos. 08/461,715 filed Jun. 5, 1995, and 08/784,985 filed Jan. 17, 1997.
2. Field of the Invention
The present invention relates to a control system/method for controlling the shifting of vehicular fully or partially automated mechanical transmission systems of the type including an engine equipped with an engine retarding device or devices, such as a compression brake, and in particular, relates to a control system/method of the above-described type which is effective to adaptively determine the optimal time to deactivate the retarding device or devices to achieve rapid and smooth upshifting.
3. Description of the Prior Art
Vehicular fully and partially automated mechanical transmission systems are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4722,248; 5,050,427; 5,136,897; 5,335,566 and 5,582,558, the disclosures of which are incorporated herein by reference.
Such fully or partially automated mechanical transmission systems typically include a microprocessor-based controller for issuing command output signals to various controllers to implement or assist selected transmission shifts, including manipulation of the engine fueling and/or of engine or input shaft brakes to cause the transmission input shaft to rotate at a substantially synchronous speed for a given output shaft speed and target gear ratio.
Engine brakes, usually called "engine compression brakes" or "exhaust brakes" are well known in the prior art and such devices, such as the well known "Jake brake," are commonly provided on heavy duty vehicles. These devices are typically manually operated, may provide variable retardation by manual selection of one, two or three banks of cylinders operation, and are utilized to retard the vehicle and, in recent developments, to quickly retard engine/input shaft speed for more rapid synchronization during an upshift. Examples of vehicular automated mechanical transmission systems utilizing automatically actuated engine brakes may be seen by reference to U.S. Pat. Nos. 4,933,850; 5,042,327; 5,409,432 and 5,425,689, the disclosures of which are incorporated herein by reference.
Generally, as is well known in the prior art, engine compression brakes are effective to alter, usually hydraulically, the engine valve timing/porting so that a relatively large compressive force and resistance is provided to rotation of the engine and the vehicle drive wheels acting through to drive axles, drive shaft, transmission and master clutch.
Other devices and techniques to selectively retard engine rotation are also known. By way of example, by increasing the load on engine-driven accessories, such as air-conditioning, the deceleration of the engine may be increased. As used herein, the term "engine braking" or like terms is intended to include such devices and/or techniques, as well as techniques involving more common engine brakes.
The prior art automated mechanical transmission systems of the type having manually and/or automatically operated engine brakes were not totally satisfactory as engine brake assisted upshifts tended to be somewhat harsh and abrupt and/or were not as rapid as desired.
In accordance with aforementioned U.S. Pat. No. 5,409,432, some of the drawbacks of the prior art were overcome by the provision of control system/method for an engine brake-equipped automated mechanical transmission system which was effective to provide relatively smooth, high-quality, rapid upshifts. By allowing automatic actuation of the engine brake, during certain upshifts, the engine brake was operated by the system controller during an upshift to exert a minimum retarding torque at initiation of the shift and to then exert a smoothly increasing retarding torque, until a maximum retarding torque value is achieved, and to exert a smoothly decreasing retarding torque upon sensing that engine rotational speed (ES) and input shaft rotational speed (IS) were within a predetermined value (about 80 to 100 RPM) of synchronous speed, which is equal to the product of output shaft speed times the numerical value of the target gear ratio (OS*GR.sub.T). The controller preferably initiated these events in advance in view of actuator response times, current values of engine speed and output shaft shaft, and/or the rates of change thereof.
A problem with the above-described and other systems utilizing automatically controlled engine braking to assist some or all upshifts was that a fixed offset or shut-off point was used to determine when to shut off the engine braking device. If the shut-off occurred too early in the shift, the upshift took too long because the transmission input shaft and associated gearing did not declerate as rapidly as desired. If the shut-off occurred too late in the shift, the input shaft and associated gearing may have decelerated too rapidly for a smooth engagement and/or may have decelerated to a speed making target ratio engagement difficult or impossible.
A problem associated with using engine retarding devices to assist upshifting is that these devices tend to have a relatively long response time (often 100-500 milliseconds) so that a command to shut off the devices must anticipate the actual optimal time to shut off the devices by several hundred milliseconds. Also, vehicle configuration (2 or 3 banks of cylinders available for compressor braking) and/or operating conditions will cause large fluctuations in vehicle retarding device performance.